This study responds to NIDA's PA-08-124 Funding Opportunity Announcement calling for research on the effects of laws, regulations and policies on the epidemiology of drug use. We propose a serial cross-sectional study to identify the impact of medical marijuana laws on drug-related attitudes, consumption and problems among adolescents and young adults. We will combine nine years of US national survey data with original data collection on the passage and characteristics of state laws. Since 1996, 17 states have passed laws that decriminalize marijuana use for medicinal purposes. Another six states are currently deliberating. Medical marijuana is intended to help patients cope with chronic pain and loss of appetite accompanying serious illness. It could, however, have unintended consequences for young people. Such policies could inadvertently send the wrong message to young people about the risks of using drugs. If poorly regulated and enforced, medical marijuana laws could increase access to illicit cannabis and drive down its price. We propose a nine-year, state-level prospective investigation of the relationships between passage of state MM laws and drug-related outcomes among youth (12-17 years of age) and young adults (18-25 years). We will use econometric methods to compare changes in drug-related attitudes and behaviors across populations of young people residing in states with medical marijuana laws, using non-medical marijuana states as a control group. We will draw on nine annual waves of the National Survey on Drug Use and Health (NSDUH), from 2002-10, augmented with original data collection on state medical marijuana laws. Proposed specific aims are: Specific Aim 1. To identify whether passage of state MM laws is associated with changing perceptions about the risks, social acceptability and availability of marijuana in populations of adolescents and young adults. Specific Aim 2. To determine whether passage of MM laws is associated with changing rates of marijuana use and problems in young people, as well as the use of economic substitutes/compliments for cannabis, such as alcohol and tobacco. Specific Aim 3. To examine whether variation across states in the characteristics and implementation of MM laws is associated with drug-related attitudes and behaviors in young people.